The present invention relates generally to power plants. More particularly, the invention concerns a method for operating a gas turbine power plant with an air reservoir cell when the air reservoir cell is empty as well as an installation for performing the method.
Gas turbine power plants with air reservoir cells have been used in the past. Typically, these gas turbine power plants include a compressor unit which supplies combustion air to a gas turbine combustion chamber as well as for filling the air reservoir cell. These units include an auxiliarly prime mover in addition to an electric power generator. During starting of the gas turbine compressor unit, the electrical generator of these known devices was electrically connected to the driving motor for the compressor unit through a power line separate from the electric power network. In a frequency acceleration mode, the compressor was accelerated from 0 rpm, i.e., from standstill, up to line frequency of the generator. When the compressor unit was operating at line frequency, the drive motor for the compressor unit was switched to the auxiliary power line so that the input drive power for the compressor unit was supplied from the auxiliary power line. During this operation, the generators could supply electrical current into the power net or could be shut down (cf. BBC Report No. 65/1975, 7/8).
With the known prior art arrangements, the auxiliary prime mover must have a high power output capacity. Accordingly an especially disadvantageous effect, namely the great economic cost, is associated with these earlier approaches.
It is an object to the present invention to provide a method and apparatus in which a relatively low capacity compressor unit for the gas turbine power plant can supply the power plant with the required combustion air when the air reservoir is empty.
The foregoing object as well as many others are solved according to the present invention by utilizing an auxiliary motor to drive a compressor unit which has at least a low pressure compressor. Compressed air from the low pressure compressor is ducted to a low pressure combustion chamber and then to a low pressure turbine component. When timing speed is attained, air in the combustion chamber is ignited along with fuel and the gas turbine power plant is accelerated to a rated speed corresponding to the line frequency. At this point, a motor-generator is switched into the power net. An advantage of the method according to the present invention is more clearly seen in that a device having a low power output capacity can be utilized as the auxiliary motor. Moreover, the auxiliary motor does not require a special auxiliary power line with the result that a special starting unit is not required.
In addition, it is possible to disconnect the gas turbine power plant from the motor-generator to pressurize the air reservoir cell. Moreover, the motor-generator can take power from the power line and switch in sequentially a medium pressure compressor and a high pressure compressor which also are components of the compressor unit. The sequential engagement of the medium and high pressure compressors depends upon the load status of the air reservoir. In a case of generator operation with an empty air reservoir cell, a high pressure turbine component of the gas turbine power plant begins operation and the compressor unit assumes sole responsibility for supply of air to the combustion chambers for the gas turbine power plant.
According to the method of the present invention, during starting of the gas turbine power plant, the medium and high pressure compressors of the compressor unit are operable to pressurize atmospheric air and supply that air to the turbine section of the gas turbine power plant.
According to another feature of the method, the high pressure turbine of the turbine section receives a reduced air flow during acceleration of the system. This reduced air flow prevents overheating in the high pressure turbine component, since the combustion chamber for the high pressure turbine has not been ignited during the acceleration.
The apparatus of the present invention includes a gas turbine power plant having a multi-section turbine and a multi-section compressor unit, both of which are arranged on a common shaft with a motor-generator. The compressor and turbine units are selectively disengageable with the motor-generator. The low pressure compressor is in fluid communication with the discharge of the low pressure compressor. In addition, the discharge outlets for the low pressure compressor, the medium pressure compressor and the high pressure compressor each communicate with the air reservoir cell as well as a high pressure combustion chamber for the turbine by means of a common duct.
The apparatus also includes a valving arrangement which permits connection of the low pressure compressor with the low pressure turbine unit while the medium pressure and high pressure compressor components discharge to atmospheric pressure during starting. As a result, a very low output capacity starting motor can be used to drive the compressor unit.